Historically, rotational position sensing has been implemented using predominantly mechanical contact-based systems. These systems are prone to break down and consequently expensive replacement over their lifetimes due to the moving parts. Alternate solutions using optical sensing are not immune to dirt and dust, which is a constraint for many industrial applications, and the like. Alternate solutions using Hall sensors rely on permanent magnets that suffer from large production variations, and hence need extensive calibration, etc.
A traditional resolver is a type of rotary electrical transformer used for measuring degrees of rotation. It is considered an analog device and consists of a stator input coil, output coil and rotor. Inductive sensing is a contactless sensing technology that offers a durable rotational position sensing implementation. This technology is extremely resistant to harsh environments along with being generally water and dirt proof, as well. In rotational sensing, the use of multiple inductance coils enables continuous 360-degree angular position sensing, and can also increase sensing accuracy.
In existing single level inductance to digital converter-based rotational resolvers system, rotational resolution is typically limited by factors such as mechanical variation s with the resolver especially along axial direction, temperature changes, conflicting requirements of resolution and speed, etc. For example, in a conventional 8192-position resolver an inductance to digital converter can only support a rotational speed on the order of 3.8 rpm; a one percent change in axial proximity may cause position error in an order of magnitude of a hundred; and when temperature changes 70 degrees C. the position error is typically on in an order of magnitude of ten.